Malaria is a leading cause of morbidity and mortality in the Third World and resistance of Plasmodium parasites to antimalarial treatments is a significant and growing problem. Novel drug targets and treatment approaches are urgently required, but this is an under-resourced problem in the pharmaceutical industry. The purpose of this proposal is to validate a malarial signaling pathway as a novel drug target, using a subset of compounds with antimalarial activity recently released by a major pharmaceutical company, together with a related group of compounds already validated for other clinical uses. The proposed target is a malarial melatonin receptor (pMTR) that is postulated to subvert the host hormone melatonin to regulate parasite proliferation and entrain the Plasmodium cell cycle to be synchronized with the host circadian rhythm. Validation of pMTR as a potential target for small molecule drug therapy would represent a paradigm shift, both in terms of the novel pathway identified and the proposed mechanism of therapeutic action. The present work is focused on the red blood cell (RBC) stage of P. falciparum infection, which is responsible for the predominant disease symptoms, including anemia, cerebral malaria, multi-organ failure and, significantly, periodic fevers that occur on a 48 h cycle. Our previous studies have provided evidence that melatonin can initiate an intracellular calcium signaling cascade involving the second messenger IP3, leading to enhanced parasitemia and stimulating progression through the cell cycle. We hypothesize that the Plasmodia melatonin receptor (pMTR) represents a novel antimalarial drug target to decrease proliferation and synchronization of the RBC cycle. The specific aims of the proposed project are: 1. To validate pMTR as a potential small molecule chemical target and assess the effects of putative pMTR modulators on P. falciparum proliferation and synchronization. These studies will determine an initial activity profile and elucidate the mechanism of drug action, while at the same time providing additional information on the pMTR signaling pathway. 2. To develop chemical probe-derived affinity reagents to identify the pMTR protein, with the eventual goal to annotate and clone the gene. 3. To determine the efficacy of pMTR modulators in combination with established antimalarial drugs that are not thought to act through the pMTR calcium signaling pathway. 4. To examine the effect of the small molecule inhibitors of pMTR identified in Aim 1 in vivo using rodent models, in order to further assess the viability of pMTR as a potential small molecule drug target. The work will be carried out by a multidisciplinary team, with expertise in calcium and G-protein signaling, malaria biology, parasitology, chemical biology and medicinal chemistry. Techniques include live-cell fluorescence imaging, imaging flow cytometry, in vivo malaria models, and synthetic chemistry. PUBLIC HEALTH RELEVANCE: This proposal investigates a unique adaptation of the malaria parasite that allows it to be concealed within red blood cells (RBCs) for much of its life cycle, and then be released in a single coordinated surge of red blood cell lysis for a brief period before reinvading other RBCs. It is proposed that the human hormone melatonin, which controls our activity level through the day/night cycle, is utilized by the malaria parasite to synchronize ts life cycle with that of the patient who is infected. We propose a strategy to validate the malarial melatonin hormone receptor as a potential target for drug therapy, using repurposing of existing drugs and a unique family of related compounds that have already been shown to have antimalarial activity.